Process for the manufacture of two or more grades of petroleum coke



PROCESS FOR THE MANUFACTURE OF TWO OR MORE GRADES OF PETROLEUM COKE Original Filed March 28, 1967 Oct. 14, 1969 D. F. CAMERON 3,472,761

GASOLINE COKER FRACTIONATOR HEAVY OIL CRACKING FURNACE GAS GASOUN E INVENTOR- DANIEL F. CAMERON ATTORNEY United States Patent U.S. Cl. 208-131 1 Claim ABSTRACT OF THE DISCLOSURE Simultaneous manufacture of two or more grades of petroleum coke by delayed coking using three or more coke drums. One drum processes a feed predominantly consisting of a regular coking feedstock such as reduced crude, to produce a regular grade of coke. Another drum processes a feed consisting predominantly of premium feedstock (such as thermal tar from a thermal cracker operating on gas oil from the coker), to produce a premium grade of coke. The two types of feed are swung from the first to the second to the third drum, so that one drum can be decoked Without interrupting continuous production of coke. Overhead streams from both or all of the operating cokers are continuously processed in a common fractiouator. Additional grades of coke can be produced by including additional coke drums, so long as the total number of drums is one more than the number of grades to be produced.

This application is a continuation of Ser. No. 627,586, filed Mar. 28, 1967, and now abandoned.

DISCLOSURE Background This invention is a process for the simultaneous manufacture of two grades of petroleum coke, by delayed coking. More particularly, the process involves the use of three coke drums, one operating on a relatively low grade of feedstock to produce a relatively low grade of coke, one operating on a feedstock of higher grade to produce a higher grade of coke, with a third drum provided so that one drum can be decoked without interrupting a continuous production of the two grades of coke. In other words, the two types of feed are swung from the first to the second to the third drum, so that one drum can be decoked without interrupting the continuous production of the two grades of coke. More than two grades of coke could also be produced by including one more drum than the number of grades to be produced.

In the art of petroleum coke manufacture there are two grades of coke. Premium coke is a high grade of coke, which, after calcination, has a relatively low coefficient of thermal expansion, and is sold for a relatively high price for use primarily in the manufacture of large metallurgical electrodes used in the steel industry. Regular coke, on the other hand, is a lower grade of coke having a relatively higher coefficient of thermal expansion which makes it unsuitable for use in the manufacture of electrodes for the steel industry but which is commonly used in the manufacture of electrodes used in the manufacture of aluminum. Premium coke is often referred to as No. 1 coke and regular coke is often referred to as No. 2 coke. The differences between premium and regular coke are further discussed in US. Patent No. 2,922,- 755.

Delayed coking is Well known and is described in the following references:

(1) Continuous Coking of Residiurn by the Delayed "ice Coking Process, R. J. Diwoky, Refiner and National Gasoline Manufacturer, vol. 17, No. 11, November 1938, heavy gas oil from delayed coking disclosed as cracking feedstock.

(2) Delayed Coking Process, Petroleum Refiner, September 1948, Foster-Wheeler Corporation.

(3) Petroleum Refiner, vol. 28 (No. 9), pp. 147-50, September 1949, Description of Kellogg Delayed Cokmg.

(4) US. Patent No. 3,257,309, particularly, FIGURE 1 and column 4, line 50-column 5, line 29.

Prior to the development of this invention, a refiner desiring to manufacture both premium and regular grades of coke would operate a conventional coker on the blocked-out basis, using different feedstocks to make each of the two grades of coke. Alternately, two separate cokers, each with its own fractionator, could be used.

Brief summary of the invention This invention is a process for the simultaneous manufacture of two or more grades of petroleum coke, by delayed coking. More particularly, the process in its preferred embodiment involves the use of three coke drums, one operating on reduced crude (or any regular coking feedstock) to produce a regular grade of coke, one operating on a feedstock consisting predominantly of premium feedstock (such as thermal tar from a conventional thermal cracker) to produce a premium grade of coke, with a third drum provided so that one drum can be decoked without interrupting a continuous production of the two grades of coke. In other words, the two types of feed are swung from the first to the second to the third drum, so that one drum can be decoked Without interrupting the continuous production of the two grades of coke. In the art of petroleum coke manufacture there are two grades of coke. Premium coke is a high grade of coke having a relatively low coefficient of thermal expansion, and is sold for a relatively high price for use primarily in the manufacture of large metallurgical electrodes used in in the steel industry. Regular coke on the other hand is a lower grade of coke having a relatively higher coeflicient of thermal expansion which makes it unsuitable for use in the manufacture of electrodes for the steel industry but which is commonly used in the manufacture of electrodes used in the manufacture of aluminum. Premium coke is sometimes referred to as No. 1 coke and regular coke is often referred to as No. 2 coke. The differences between premium and regular coke are further discussed in US. Patent No. 2,922,- 755. The overhead streams for both or all of the operating cokers are continuously processed in a common fractionator.

The drawing The drawing shows a simplified process flow diagram illustrating the process.

Detailed description Virgin reduced crude, preferably preheated by heat exchangers (not shown) is introduced through line 1 into combination furnace 2 wherein it is further preheated in the convection section of the furnace. The reduced crude, at a temperature of about 800 F., is then preferably passed through line 3 to flash tower 4. The overhead from the flash tower is passed through line 5 to condenser 6 from which a portion of the resulting gas oil is refluxed through line 7, the remainder of the gas oil being pumped through line 8 to the thermal cracker fractionator 9. The flash tower bottoms are pumped through line 10 to the furnace 2 and then to switch valve 11, from which the feed is introduced into one of the coke drums 12. The flash tower is not essential and could be eliminated from the process design.

Hot unstripped thermal tar from the 'bottom of the thermal cracker fractionator 9 is simultaneously fed to the coker fractionator 13 through line 14. The thermal tar (containing some thermal cycle oil and some regular coker gas oil) from the bottom of the coker fractionator 13 is fed to the furnace 2 through line 15 and into one of the other coke drums through a conventional switch 'valve 16. A portion of the regular coke feedstock is preferably combined with the thermal tar by means of line a to provide a feedstock blend having about 10 to about 30 percent by weight of virgin reduced crude. As indicated in US. Patent No. 2,922,755, such a blend will produce premium coke. Additional quantities of reduced crude could be used if it is desired to produce intermediate and regular grades of coke rather than premium and regular grades.

Suitable coking conditions are 850950 F. and 20-80 p.s.i.g.

The overhead streams from the two operating coke drums are combined and passed to the coker fractionator 13 through line 17. The overhead from the coker fractionator is separated into gas and gasoline as shown in the drawing.

A light gas oil is passed from the coker fractionator through line 18 to surge drum 19, and heavy gas oil is fed from the coker fractionator to surge drum 21 through line 20. Lines 22 and 23 are used to vent surge drums 19 and 21, respectively. These vents are connected to any low pressure area of the system; for example, they can be tied into the coker fractionator 13. Light gas oil from surge drum 19 is combined with the gas oil from line 8 and is fed to thermal cracker fractionator 9 through one or both of lines 24 and 25. Heavy gas oil is fed to the fractionator through line 26.

Gas and gasoline are recovered from the overhead of the thermal cracker fractionator 9 as shown in the drawmg.

A light gas oil is pumped to light oil cracking furnace 28 through line 27, wherein it is cracked utilizing an inlet temperature of about 650 to 750 F. and an outlet temperature of about 950 to 1050 F. The eflluent from furnace 28 is passed back into the bottom of the fractionator 9 through line 29. A heavy gas oil is pumped to heavy oil cracking furnace 31 through line 30, wherein it is cracked utilizing an inlet temperature of about 700 to 800 F. and an outlet temperature of about 875 to 975 F. The efiluent from furnace 31 is returned to the bottom of the fractionator 9 through line 32. As indicated previously, the bottoms from the fractionator 9 are pumped, preferably without stripping, to the coker fractionator 13 which serves as a combination tower, i.e., to quench the coke drum efiluent 17 and to flash thermal cracker fractionator bottoms 14. Conventional thermal cracking units include a flash tower to strip the thermal tar.

The operation of the coker is preferably based on a coke drum cycle of 48 hours. This provides for a 16hour decoking cycle in conjunction with 32 hours of on-stream operation. When a drum of coke is filled with a mass of coke, it is opened top and bottom and the coke is removed by cutting -it out with high velocity water jets. In accordance with conventional practice, the total time required for preparing the drum for decoking and readying the drum for operation, is normally about 16 hours.

EXAMPLE Fresh feed (line 1): 630+ F. Minas reduced crude 11,120 b.p.s.d.)

4 Temp. line 1 at inlet furnace 2: 700 F. Temp. line 3: 810 F. Flow rate line 5: 44,460 lb./hr. hydrocarbon; 3,715 lb..

hr. steam Flow rate line 8: 2,930 b.p.s.d. Line 10:

Specs.17.8 API; Flow rate8,320 b.p.s.d. Line 15:

Specs.Gravity 7.8 API; Flow rate7,900 b.p.s.d. Flow rate line 10a: 1,080 b.p.s.d. Pressure in coke drums: 50 p.s.i.g. Temperature of feed to coke drums: 925 F. Outlet temperature line 17 from coke drums: 825 F. Green regular coke production: 186 short tons/stream day Green premium coke production: 234 short tons/stream day Line 14:

Flow rate--11,240 b.p.s.d. Specs.Gravity, 17.8 API Flow rate line 17: 198,000 lb./hr. Flow rate line 18: 3,920 b.p.s.d. Flow rate line 20: 10,330 b.p.s.d. Line 24:

Flow rate20,000 b.p.s.d. Specs.Gravity, 29.5 API Inlet to furnace 28-700 F; 1245 p.s.i.g. Outlet of furnace 28-1000 F.; 750 p.s.i.g. Line 30:

Flow rate-25,000 b.p.s.d. Specs.Gravity, 26.0 API Inlet to furnace 31-740 F.; 1350 p.s.i.g. Outlet of furnace 31925 F.; 500 p.s.i.g.

I claim:

1. A process for the simultaneous production of two grades of petroleum coke comprising the steps of: providing three delayed coking zones; producing premium coke alternately and sequentially in each of said zones utilizing a feedstock predominantly comprising thermal tar from a thermal cracker, the feed to said thermal cracker comprising gas oils from said coking zones; producing regular coke alternately and sequentially in each of said zones utilizing a feedstock predominantly comprising a virgin reduced crude; alternating and sequentially removing said coke from said coking zones; passing the overhead vapors from both of the operating coking zones into a common fractionator; passing unstripped thermal tar from said thermal cracker into said fractionator; and utilizing the bottoms (thermal tar) from said fractionator as premium feedstock for said premium coking operation as aforesaid.

References Cited UNITED STATES PATENTS 2,199,759 5/1940 Schnetzler 2081 31 2,380,713 7/1945 Wilson 208131 2,922,755 1/ 1960 Hackley 208106 3,072,561 1/1963 Cahn 208141 2,322,863 6/1943 Marschner et al 20879 HERBERT LEVINE, Primary Examiner US. Cl. X.R. 

